Transcript Site Decontamination through Excavation/Dredging

Ex Situ Treatments
Following Dredging and/or Excavation
Method
Comments
Dewatering
Extraction of water from removed sediment
Particle separation
Selective removal of sediments (e.g., fine particles)
that contain relatively high concentrations of
trace metals
Soil washing
Extraction of metals from the sediments using a
water-based solvent which may or may not be
combined with other reagents
Vitrification
Heating of contaminated materials to high
temperatures to produce a glass-like nonleachable material with low-permeability
Solidification-stabilization
Addition of binding agents to produce a hardened
material of low-permeability
In Situ Treatments
Phytoremediation
Use of plants to extract trace metals from the soils
and sediments
In situ vitrification
Same as above, but heat source is typical produced
by an electrical current delivered through electrodes
In situ soil washing
Same as above, with the exception that solutions are
applied and extracted to in situ materials
Encapsulation
Encasing of contaminated material with a lowpermeability substance
Electrokinetics
Use of an electric current to concentrate and remove
ions
In situ (subaqueous) capping
The placement of a clean, isolating material over
contaminated sediment in a subaqueous
environment without relocating or causing a major
disruption to the original channel bed material
Soil and sediment capping
The placement of clean material over contaminated
sediment out in a subareal environment
Site Decontamination through
Excavation/Dredging
• The most commonly used remediation
strategy
• Favored because:
– (1) it has been shown to be an effective remedial technology
in a wide range of riverine and marine environments.
– (2) it is consistent with recent legislation which favors
remedial technologies that permanently reduce the volume,
toxicity or mobility of the contaminant of concern.
Definitions
• Excavation is defined as the subareal extraction
of sediment using earthmoving equipment (e.g.,
as backhoes and front-end loaders)
• Dredging refers to the extraction of sediment
from an underwater environment (NRC 1997).
– Environmental Dredging: conducted to remove
contaminated sediment
– Navigational Dredging: conducted to maintain
navigable channels and other facilities
Use
• Has been used at about 100 Superfund Sites across the country;
most have targeted sites with less than 50,000 yds3 of material
(Romgnoli et al., 2002)
• The volume of material removed during these operations can vary
dramatically, ranging from 101 to 106 m3.
• Following the Aznalcóllar tailings dam failure in Spain, for example,
more than 4.7 x 106 m3 of tailings and contaminated sediment was
removed from along the Rios Agrio and Guadiamar in 1998-1999 as
part of an emergency cleanup operation (Hudson-Edwards et al.
2003).
• In the U.S., Cleland (2000) found in a study of 89 completed,
ongoing, or planned sediment cleanup projects in the U.S., that
approximately 1.4 million cubic yards of material had been removed
by dry excavation methods.
Advantages of
Dredging/Excavation
•
Decontamination of the site generally;
•
Allows for greater flexibility in land-use.
•
Perceived as having a lower risk of failure
than other methods;
•
Can be conducted in a predictable time
frame;
•
Costs can be predicted reasonably well.
Other Considerations of
Dredging/Excavation
•
Quantity of material to be excavated – it can be
very expensive;
•
Where will the material go (CDF, CAD, existing
landfill)?
•
Permission and license requirements
•
Resuspension and environmental degradation
problems
•
Questions regarding effectiveness of
decontamination process
Air or Gas Residue
Treatment
Flow Diagram for Dredging and Excavation
Debris
Removal
Sediment
Removal
Transport
Staging
Pretreatment
Contaminated
Solids
Treatment
Water Effluent
Treatment and/or
Disposal
Figure 6-1, page 6.1, in USEPA, 2005, Contaminated sediment
remediation guidance for Hazardous Waste Sites. EPA-540-R-05-012,
OSWER 9355.0-85. No permission required.
Disposal and/
or Reuse
ed
at
in
m s
ta lid
on So
C
Solids
Disposal and/
or Reuse
Figure 3 and 4, page 186, from Romagnoli, R.,
Doody, J.P., VanDewalker, H.M., and Hill, S.A., 2002.
Environmental dredging effectiveness: Lessons
Learned. In: A. Porta, R.E. Hinchee, and M. Pellei
(eds.), Management of Contaminated Sediments,
Battelle Press, Columbus, Ohio.
(A)
Date
0.00
10/7/99
10/9/99
10/11/99
10/13/99
10/5/99
9/29/99
10/1/99
10/3/99
9/25/99
9/27/99
9/21/99
9/23/99
9/17/99
9/19/99
9/11/99
9/13/99
9/15/99
9/9/99
9/7/99
9/1/99
9/3/99
9/5/99
8/28/99
8/30/99
(B)
1/18/99
1/14/99
1/10/99
1/2/99
1/6/99
12/29/98
12/25/98
12/21/98
12/17/98
12/13/98
12/9/98
12/5/98
12/1/98
11/27/98
11/23/98
11/19/98
11/15/98
11/11/98
11/7/98
11/3/98
10/30/98
10/26/98
10/22/98
0
8/24/99
8/26/99
D/U Ratio
D/U Ratio
Maximum = 33 on 1/20/1999
14
12
10
8
6
4
2
Date
4.00
3.50
3.00
2.50
2.00
1.50
1.00
0.50
Figure 1, pg. 1 in J.J. Steuer (2000). A mass-balance approach for assessing
PCB movement during remediation of a PCB-contaminated deposit on the Fox
River, Wisconsin. USGS Water-Resources Investigations Report 00-4245.
Average Concentration (mg/kg)
60
54
3-Week Caged Fish
50
6-Week Caged Fish
41.3
40
35
30
20
11
11
11
10
6.5
5.0
3.1
0
0.6
2.8
0.2
2.0
1.1
0.13
1.1
2.7
0.39
0.5
2.2
0.38
0.64
0.22
0.23
Downstream Downstream Upstream Upstream Downstream Downstream Upstream Upstream
Near Short
Far Shore Near Shore Far Shore Near Short
Far Shore Near Shore Far Shore
Pre-dredging
During dredging
Figure 1, page 183, from Romagnoli, R., Doody, J.P., VanDewalker, H.M.,
and Hill, S.A., 2002. Environmental dredging effectiveness: Lessons
Learned. In: A. Porta, R.E. Hinchee, and M. Pellei (eds.), Management of
Contaminated Sediments, Battelle Press, Columbus, Ohio.
Post-dredging
Degree of Residual Contamination
Change in Concentration (μg/g)
Preremediation
PostRemediation
Percent
Change
PCBs
--Average
--Maximum
518
1,780
75
260
86
85
PCBs
--Average
--Maximum
640
4,500
39
295
94
93
PCBs
--Maximum
1,400
136
90
PCBs
--Average
--Maximum
200
8,800
9.2
<100
95
99
Lower Fox River, WI
(Deposit N)
PCBs
--Average
--Maximum
16-130
61-186
14
130
12-89
0-30
Lower Fox River, WI
SMU 56/57
PCBs
---Maximum
710
17
98
Manistique River, MI
PCBs
---Maximum
4,200
1300
69
Site
Grasse River, NY
Sheboygan River, WI
River Raisin, MI
St. Lawrence River, NY
Contaminant
From Miller JR and Orbock Miller, SM: 2007, Contaminated Rivers, Springer
Figure 6-8, p. 6-28, USEPA (2005) Contaminated Sediment Remediation
Guidance for Hazardous Waste Sites. EPA-540-R-05-012.
Soil Washing
• Soil washing is a general term used for the
extraction of a wide range of organic and inorganic
contaminants from soils and sediment using a waterbased fluid as a solvent
• Two Basic Components
– Particle separation of excavated materials;
– Leaching of contaminants from sediments/soils in
situ or that have been excavated.
Particle Separation
of Excavated Materials
•
Assumes that contaminants are segregated with
one size fraction of the alluvium which can be
separated and disposed of separately;
•
General idea is to remove the contaminated
fraction – which in most cases is the fine-grained
sediment – and return the coarser,
uncontaminated sediment to the site. This
reduces the overall amount of material that must
be disposed of in a landfill or other type of
disposal facility;
•
These methods can be relatively expensive - $1.5
M per hectare.
Particle Separation
of Excavated Materials
• Variety of engineering methods exist to
remove the fine fraction; these include
sieving, flotation techniques, hydrocyclones,
fluidized-bed separation, or spiral classifiers.
Rulkens et al., 2003
Leaching Methods of Soil Washing
•
Method is not all that commonly used
in U.S., but is used in EU. Likely to be
used in U.S. more in future. Can be
expensive.
•
Chemicals that are used include
inorganic acids, organic acids, and
complexing agents such as EDTA, or
a combination of these chemicals.
Requires that the soils are permeable, thus favors coarser-grained sediments.
Figure 1, page 112, in Krishnan, R. Parker, H.W., and Tock, R.W., 1996.
Electrode assisted soil washing. Journal of Hazardous Materials 48:111119.